Automatic Defect Classification (ADC) techniques are widely used in inspection and measurement of defects on patterned wafers in the semiconductor industry. ADC techniques detect the existence of defects, as well as automatically classify the defects by type in order to provide more detailed feedback on the production process and to reduce the load on human inspectors. ADC techniques are used, for example, to distinguish among types of defects arising from particulate contaminants on a wafer surface and defects associated with irregularities in the microcircuit pattern itself, and may also identify specific types of particles and irregularities.
Current approaches of defect classification use computer-aided design (CAD) data together with images of a semiconductor device under inspection. For example, U.S. Pat. No. 7,626,163 describes a defect review method in which a scanning electron microscope (SEM) image is derived by capturing an image of a process-margin-narrow pattern portion extracted based on lithography simulation with image-capturing conditions of a relatively low resolution. The resulting SEM image is compared with CAD data for extraction of any abnormal section. An image of the area extracted as being abnormal is captured again, and the resulting high-resolution SEM image is compared again with the CAD data for defect classification based on the feature amount of the image, such as shape deformation.
A number of techniques are known in the art for three-dimensional (3D) mapping of samples using SEM images. For example, U.S. Pat. No. 6,930,308, which is hereby incorporated by reference, describes a technique for inspecting semiconductor devices. The technique utilizes multiple sets of measurement data obtained by a SEM to determine the dimensional parameters of a semiconductor device. The SEM collects each set of data from a different angular orientation with respect to the device. The dimensional parameters of the semiconductor device are determined by analyzing the relationship between the SEM inspection angle and the collected data sets.
As another example, U.S. Pat. No. 7,705,304, which is hereby incorporated by reference, describes a 3D shape measurement in which detection signals from respective semiconductor elements are sequentially switched in synchronization with a scanning frame of an electron beam on a sample. The detection signals from the respective semiconductor elements can be sequentially recorded in recording addresses in a frame memory that correspond to the respective semiconductor elements. After four electron beam scanning sessions, each image data for 3D shape measurement is recorded in the frame memory, and processed for 3D shape measurement.